Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
J Phys Chem B. 2024 Aug 8;128(31):7558-7567. doi: 10.1021/acs.jpcb.4c03917. Epub 2024 Jul 29.
Hemoglobins achieve cooperative oxygen binding by diverse strategies based on different assemblies of globin subunits. Heterotetrameric hemoglobin from (HbII) consists of two AB-dimers, whose structure closely resembles that of homodimeric hemoglobin from the same organism (HbI). Herein, we investigated the structural dynamics of HbII following carbon monoxide (CO) dissociation using time-resolved resonance Raman (RR) spectroscopy. The observed spectra showed that the heme structure of the transient dissociated form of HbII was similar to that of HbI; however, the transition from the transient dissociated form to the equilibrium unligated form was faster for HbII than for HbI. Furthermore, the dependence of the time-resolved spectra on the yield of CO dissociation revealed that the transition became faster as the number of dissociated ligands increased from one to four. The positive correlation between the rate constants and number of dissociated ligands indicates that the structural transition of HbII following CO dissociation is cooperative.
血红蛋白通过不同的策略实现协同氧结合，这些策略基于球蛋白亚基的不同组装。来自 （HbII）的异四聚体血红蛋白由两个 AB-二聚体组成，其结构与来自同一生物体的同源二聚体血红蛋白（HbI）非常相似。在此，我们使用时间分辨共振拉曼（RR）光谱研究了 CO 解离后 HbII 的结构动力学。观察到的光谱表明，HbII 的瞬时解离形式的血红素结构与 HbI 相似；然而，HbII 从瞬时解离形式到平衡未配位形式的转变比 HbI 更快。此外，时间分辨光谱对 CO 解离产率的依赖性表明，随着从一个到四个的解离配体数量的增加，转变变得更快。速率常数与解离配体数量之间的正相关性表明，CO 解离后 HbII 的结构转变是协同的。
